1. Field of the Invention:
The present invention relates to improvements in the field of hydraulically actuated poppet valves.
2. Description of Related Art:
Hydraulic actuation of the intake and exhaust valves of internal combustion engines offer significant improvement compared to mechanical actuation in many aspects of engine performance. Hydraulic actuation, combined with computer control, permits flexibility in valve scheduling not possible with camshafts.
Several different designs of hydraulically actuated valves have been advanced. Some designs use hydraulic pressure to both open and close the valves. The poppet valve includes a piston integral with its valve stem. High-pressure hydraulic fluid applied to one side of this piston opens the valve. High pressure hydraulic fluid on the other side of the piston creates a force in the direction of closing the valve. The valve is opened by an application of high-pressure fluid during the initial portion of the opening stroke to obtain a high opening velocity, followed by reliance on the valve's inertia to complete the opening. The valve is held open by hydraulic lockup of fluid on one side of the piston. Release of this lockup of fluid a low-pressure reservoir permits high-pressure fluid on the closing side of the piston to accelerate the valve toward the closed position. When the valve closing velocity is suitably high, fluid on top of the piston is momentarily locked again. As the valve slows, some of its inertia is traded for creation of high-pressure hydraulic fluid, which is returned to the high-pressure reservoir. Release of the lockup permits the poppet valve to complete the closing cycle. This class of hydraulically actuated valves requires a precisely machined piston integral with the valve stem. Also, the engine cylinder head must either be heavily modified or specially designed to accommodate the piston. U.S. patents incorporating this type of operation include 5,456,223 to Miller et al., and 5,255,641, 5,275,136, and 5,456,222, all to Schechter.
Another variety of hydraulically actuated valves incorporates a spring. Some designs incorporate the spring to bias the poppet valve to the closed position. At least one design incorporates a spring that biases the valve to a position intermediate of fully opened or fully closed. Some designs incorporate pistons integral with the valve stems, while others use a separate piston on top of the valve stem.
Some of these designs operate with a single source of hydraulic fluid at high pressure, maintaining the high pressure during the entire valve opening period. In some cases, the high-pressure fluid is released to an atmospheric pressure sump during valve closing. Either of these approaches can be costly to the overall performance of the engine by requiring large amounts of high-pressure hydraulic fluid. Some designs require hydraulic spool valves, a metering system, or two serial stages of valves for proper operation of the poppet valve. These additional valves increase the cost and complexity and lower the reliability of the overall valve actuation system.
Patents showing hydraulically-actuated poppet valves with return springs include U.S. Pat. No. 5,517,951 to Paul et al.; 5,022,358 and 5,248,123 to Richeson; 4,206,728 to Trenne; and Japanese Patent No. 188016 to Yamagawa et al.
To make hydraulically-controlled poppet valves commercially viable on internal combustion engines, the disadvantages of the related art must be overcome. For example, it is desirable to incorporate hydraulically-actuated poppet valves with minimal changes required to the cylinder head. Mechanical complexity and associated costs can be minimized by utilizing a spring to return the poppet valve to the closed position. It is further desirable to minimize use of high-pressure fluid during actuation of the poppet valve and to incorporate methods of recovering energy during operation of the valve. It is also desirable to use a pressure control means for applying pressure to the actuator with simple on and off states, requiring neither metering of fluid nor additional valves. No invention of the related art incorporates all these features.
The present invention provides a novel and unobvious answer to many of the problems of making hydraulically-actuated poppet valves commercially viable. Use of a valve spring for closing force reduces the cost of incorporating hydraulically-actuated poppet valves on existing cylinder heads. Control of actuation pressure is achieved with either a simple two-position valve or a simple three-position valve. Two methods of energy recovery are shown. The present invention is the first to incorporate all of these advantages.